1. Field of the Invention
The present invention relates to an image capture device, an image capture apparatus, a signal processing method, and a program which are preferably applied to, for example, a case in which noise components superimposed on output signals of the image capture device are eliminated.
2. Description of the Related Art
Various technologies have been proposed in order to correct noise components (particularly, dark current noise or low-frequency fixed-pattern noise in columns and lines) superimposed on image signals output from a solid-state image capture device. One example of a technology for noise correction using optical black pixels (hereinafter may be referred to as “OB pixels”) or dummy pixels for outputting pseudo image signals generated by only analog-to-digital conversion regardless of the presence/absence of pixels. Image signals output from those pixels are read pixel by pixel in the same manner as valid pixels for generating analog image signals (which, together with digital image signal described below, may hereinafter be referred to as “image signals”) when image light of a subject is incident. A signal processing device for processing image signals output from the solid-state image capture device determines an average value of signal levels of the image signals for each area, such as a column, a line, or an entire surface of an OB pixel area, and performs noise correction using the average value as a noise correction value.
Since the noise correction value used is merely the average value, no special processing has been performed in order to transfer image signals output from the OB pixels or dummy pixels.
In recent years, however, since the number of pixels processed by each image capture apparatus has increased and the frame rate also has increased, the band of transferring image signals has become higher. Thus, when the transfer band of the image signals is increased with the signal processing device having a typical configuration as described above, the power consumption increases.
An example of the configuration of an image capture apparatus 100 of related art will now be described.
FIG. 16 is a block diagram showing an example of the internal configuration of the image capture apparatus 100 of related art.
The image capture apparatus 100 includes a solid-state image capture device 101 and a signal processing device 105. The solid-state image capture device 101 outputs digital image signals and the signal processing device 105 receives the digital image signals from the solid-state image capture device 101 and performs predetermined correction processing on the digital image signals.
The solid-state image capture device 101 includes pixel units 102 for outputting analog image signals obtained from subject image light that is incident via a lens (not shown). The solid-state image capture device 101 further includes an analog-to-digital converting unit (A/D) 103 for converting the analog image signals, received from the pixel units 102, into digital image signals and a digital processing unit 104 for performing predetermined processing on the digital image signals.
The signal processing device 105 has a noise correcting unit 106 for correcting noise superimposed on the digital image signals. The noise correcting unit 106 includes a delay unit 107 and an average-value determining unit 110. The delay unit 107 delays output of the digital image signals, input from the solid-state image capture device 101, by a predetermined amount of time and the average-value determining unit 110 determines an average value of the levels of the digital image signals per unit time. The noise correcting unit 106 further includes a correcting unit 108 for performing predetermined correction on the digital image signals input from the delay unit 107 and the average-value determining unit 110.
The average-value determining unit 110 includes an adding unit 111 for adding the signal levels of the digital image signals, output from the solid-state image capture device 101, a predetermined number of times and a counter 112 for measuring the number of times the addition is performed by the adding unit 111. The average-value determining unit 110 further includes a dividing unit 113 for dividing the digital-image-signal signal level, added by the adding unit 111, by the number of additions measured by the counter 112. An output of the dividing unit 113 is input from the average-value determining unit 110 to the correcting unit 108. The correcting unit 108 then performs noise correction on the digital image signals by subtracting the average value, input from the average-value determining unit 110, from the digital image signals input from the delay unit 107.
FIG. 17 illustrates one example of pixel areas of the solid-state image capture device 101.
The number of pixel units 102 and the number of analog-to-digital converting units 103 in the solid-state image capture device 101 correspond to 2160×1160 words, more specifically, 2160 words in a horizontal direction and 1160 words in a vertical direction. A valid pixel area 121 is provided to output analog image signals in response to incident image light. An optical black (OB) pixel area 122 is provided in a light-shielding area around the valid pixel area 121. Since no image light is incident on the OB pixel area 122, the OB pixel area 122 outputs analog image signals regardless of image light. The image signals output from the pixel units 102 provided in the OB pixel area 122 are used to eliminate noise components and so on superimposed on the image signals output from the valid pixel area 121.
A dummy pixel area 123 is provided around the OB pixel area 122 to output pseudo analog image signals. The dummy pixel area 123 has no pixel units 102 and has only the analog-to-digital converting units 103, and is thus used to detect analog characteristics other than those of the pixels. For example, for a column A/D structure, the dummy pixel area 123 has analog-to-digital converting units 103 corresponding to the number of pixels in one line. Thus, the dummy pixel area 123 physically has the analog-to-digital converting units 103, the number thereof corresponding to the number of pixels (i.e., 40 pixels), at each of the left and right sides of the valid pixel area 121, so that image signals are read from the dummy pixel area 121 as in the valid pixel area 121 having pixels. The pixels located at each of the upper and lower sides of the valid-pixel area are 121 isolated and mage signals corresponding to 40 lines at each of the upper and lower sides are repeatedly read. This reading corresponds to reading image signals from the dummy pixels corresponding to 40 pixels from the upper, lower, left, and right pixel areas.
The pixel areas shown in FIG. 17 represent a transfer scheme of the image signals, not a physical pixel arrangement. More specifically, FIG. 17 shows a transfer scheme for a case in which the valid pixel area 121 occupies an area of 2000×1000 words and the OB pixel area 122 occupies an area of 40 words at each of the upper, lower, left, and right sides of the valid pixel area 121. In addition, the dummy pixel area 123 corresponding to 40 words is physically provided at each of the left and right sides and no dummy pixel area is provided in each of the upper and lower sides of the valid pixel area 121. In the transfer scheme, however, image signals corresponding to 40 words are read from each of the upper, lower, left, and right sides of the dummy pixel area 123. With this arrangement, the solid-state image capture device 101 in the related art transfers pixel data containing analog image signals corresponding to 2,505,600 (=2160×1160) words to the signal processing device 105 for each horizontal line (i.e., for each set of 2,160 words).
When attention is given to an image output for each line in the vertical direction, the image output can be expressed in the following manner.
For simplicity of representation, the number of words of image signals output from each pixel area is expressed by a combination of the name of the pixel area and the number of words.
1 to 40 lines: dummy 2160 words
41 to 80 lines: dummy 40 words, OPB 2080 words, and dummy 40 words
81 to 1080 lines: dummy 40 words, OPB 40 words, valid 200 words, OPB 40 words, and dummy 40 words
1081 to 1120 lines: dummy 40 words, OPB 2080 words, and dummy 40 words
1121 to 1160 lines: dummy 2160 words
Although a description below is given in conjunction with an example of correcting image signals output for each line, correction of image signals output for each column is also performed. Correction for each column uses data for each column.
FIG. 18 illustrates an example of noise detection and correction processing on the pixel data, the noise detection and the correction processing being performed by the image capture apparatus 100 in the related art through use of the dummy pixels.
Now, a description will be given with reference to the enlarged view of an area 124 (shown in FIG. 17) in the solid-state image capture device 101.
A horizontal line 125 includes analog image signals output from the valid pixel area 121, the OB pixel area 122, and the dummy pixel area 123.
The adding unit 111 included in the signal processing device 105 adds digital image signals, output from the dummy pixel area 123 and converted, a predetermined number of times. Using the number of additions measured by the counter 112, the dividing unit 113 determines an average value by dividing the result of the addition. The correcting unit 108 then performs noise correction on the digital image signals obtained by converting analog image signals output from the valid pixel area 121 on the same horizontal line, by performing processing, such as subtracting the average value.
FIG. 19 illustrates an example of a scheme for transferring, in one horizontal line 125, pixel data contained in the pixel data output from the solid-state image capture device 101.
The horizontal line 125 for the image signals output from the solid-state image capture device 101 to the signal processing device 105 has a structure as described below. The pixel data containing the analog image signals output from one pixel unit 102 included in the horizontal line 125 has a data width of 12 bits, and is represented by u10.2. Thus, the analog image signals output from the dummy pixel area 123 and the analog image signals output from the pixel units 102 included in the OB pixel area 122 and the value-pixel area 121 are represented by u10.2 for each pixel. In this case, in the representation “u10.2”, “u” means “unsigned” and “10.2” means that the integer portion is 10 bits and the fractional portion is 2 bits. This representation is used in the description below.
As illustrated in FIG. 19, the horizontal line 125 includes analog image signals output from the 40-word dummy pixel area 123, the 40-word OB pixel area 122, and the 2000-word valid-pixel area 121. In the illustration in FIG. 19, however, attention is given to only the area 124. In practice, the horizontal line 125 further includes pixel data output from the 40-word OB pixel area 122 and the 40-word dummy pixel area 123 located at the right side of the valid pixel area 121.
Japanese Unexamined Patent Application Publication No. 2007-235889 discloses a technology for performing data correction by using data read from an optical black section and a dummy pixel section.
Japanese Unexamined Patent Application Publication No. 2007-243637 discloses a technology in which a reference signal that acts as a reference for clamping is controlled in accordance with sensitivity setting to thereby reduce the amount of color phase shift and so on found in a low-luminance portion and caused by noise clipping.
Japanese Unexamined Patent Application Publication No. 2008-206003 discloses a technology in which the values of dummy pixels are subtracted from the values of valid pixels to thereby eliminate an influence of power-source noise and so on.